1. Field of the Invention
The present disclosure relates to a touch display device, and more particularly, to a touch panel for a touch display device and a method of fabricating the same.
2. Description of Related Art
With rapid development of information technologies, display devices for displaying a large amount of information have been promptly developed. More particularly, flat panel display (FPD) devices having a thin profile, light weight and low power consumption such as organic electroluminescent display (OLED) devices and liquid crystal display (LCD) devices have been actively pursued and widely applied.
Recently, touch display devices, which include a touch panel attached on a display panel, have been spotlighted.
The touch display devices, which may be referred to as touch screens, are used as an output means for displaying images and also used as an input means for receiving instructions from a user. Namely, when a user touches the touch panel while watching an image displayed by the display panel, the touch panel detects location information about the touch point and compares the detected location information with location information of the image, thereby performing an instruction from the user.
Touch panels are classified into various types according to different methods of detecting a touch input of a user, including resistive type, capacitive type, infrared type, and surface acoustic wave type.
Among these types, capacitive type touch panels have been widely used because of their superior durability, long life time, facile multi-touch, and high transmittance.
The capacitive type touch panels are classified into mutual capacitance type and self-capacitance type. In the mutual capacitance type, driving lines and sensing lines are independently formed, and changes in capacitance between the driving lines and the sensing lines are detected according to touches. In the self-capacitance type, voltages are applied to touch electrodes, which are independently formed in respective regions, and changes in capacitance of the touch electrodes are detected according to touches.
A touch display device including a touch panel may be fabricated by attaching an additional touch panel to a display panel or by forming elements of a touch panel on a substrate of a display panel such that the touch panel is one united body with the display panel.
Hereinafter, a touch display device including a mutual capacitance type touch panel will be described with reference to FIG. 1.
FIG. 1 is a schematic view illustrating an in-cell or on-cell type touch display device with an integrated touch panel according to the related art. Alternatively, the related art touch display device may include an add-on type touch panel. Here, an organic light-emitting diode display device is used as a display panel, and a touch panel is a mutual capacitance type.
In FIG. 1, the related art touch display device includes a display panel 10, a touch panel 30 and a polarizer 40. A first surface of the touch panel 30 is attached to the display panel 10 by an adhesive layer 20, and a second surface of the touch panel 30 is attached to the polarizer 40.
The display panel 10 includes a first substrate 12 on which a thin film transistor and an organic light-emitting diode including a cathode electrode 14 are formed. An encapsulation layer 16 is formed on the cathode electrode 14.
The touch panel 30 includes a second substrate 32, first lines 34a and second lines 34b on a surface of the second substrate 32, and an insulating layer 36 covering the first and second lines 34a and 34b. 
Here, light emitted from the organic light-emitting diode is outputted to the outside through the cathode electrode 14, the touch panel 30 and the polarizer 40, thereby displaying an image.
In the meantime, each first line 34a and each second line 34b cross each other to form a mutual capacitor. When a user touches the touch display device, mutual capacitance of the mutual capacitor varies, and a touch point is detected from the varied mutual capacitance.
In addition, in the related art touch display device, since the first lines 34a and the second lines 34b are disposed close to the cathode electrode 14, parasitic capacitance is generated due to the cathode electrode 14. The parasitic capacitance changes due to noise from an image signal, which is applied to the cathode electrode 14, and the touch performance decreases.
The parasitic capacitance varies according to a thickness of the adhesive layer 20. As the thickness of the adhesive layer 20 becomes thin, a distance between the first and second lines 34a and 34b and the cathode electrode 14 becomes short, and the parasitic capacitance increases. Thus, the touch performance rapidly decreases. For instance, the signal to noise ratio (SNR) is 35 dB when the thickness of the adhesive layer 20 is 35 micrometers, and the SNR is 25 dB when the thickness of the adhesive layer 20 is 10 micrometers. Accordingly, the thinner the thickness of the adhesive layer 20 is, the larger the noise is, and the touch performance is reduced.